synthetic gear oil?

[johnnybronco]

I just had my 5-speed rebuilt and the mechanic suggested synthetic gear oil. Anybody have an opinion or a suggestion as to what kind to buy? I saw it for $20/quart at Advance Auto parts - that's $100 bucks to top off my tranny and I'm not sure if I need to spend that kind of money.

 

[Captain Ledd]

I've read that the super slippery stuff in a manual can make the synchro's not work particularly well, and be difficult to shift. Instead of synchronizing, they just slip and take a long time to match speeds.

I've never tried it. I'd just go with good quality regular oil personally. I mean, yeah you just had it rebuilt, but it's a what? 24 year old transmission at this point?

By the time it goes kabang again it'll long be a classic. And M5OD's will still probably be around... *edit: To replace it with*

 

[shane96ranger]

M5OD, correct? Use ATF.

Oh.... it doesn't take 5 quarts either. It's about 3 3/4 quarts.

 

[Captain Ledd]

1989 = FM-146
4.8 pints 80W90 Gear oil.

 

[shane96ranger]

My Buddy has an 89 with an M5OD in it, factory.

 

[johnnybronco]

Ok - took my '90 M50D and a '90 2.9 and put
em in an '89 body. And I used ATF on it before.

 

[Captain Ledd]

AHH, then yes. ATF it is. Just about any will do, technically you should really make sure it's specified for Mercon though.

 

[johnnybronco]

Thanks everybody!

 

[johnnybronco]

And you can pour it straight in through the top where the shifter attaches?

 

[shane96ranger]

Yes sir.

 

[snake]

You can pour it through the top but keep the top fill plug out while pouring so it won't be overfilled.

 

[johnnybronco]

Looks like the capacity is 3 and 3/4 quarts. You don't think I can just pour that much in and not worry about it?
I just had it re-built so it is bone-dry.

 

[Captain Ledd]

A little too much oil is better than not enough. 1/4 of a quart is not a whole lot of oil. Especially once it's spread out over the whole area of the internal case. So you might have an extra 1/8-1/4" of oil in the case?

Dump it all in and call it good. I did the same thing with my 8.8 gear oil. Got 3 quarts even though it didn't need that much. What am I going to do with the rest of the 1/2-1/4 quart of oil? Save it for YEARS?

 

[AgPete139]

I've read that the super slippery stuff in a manual can make the synchro's not work particularly well, and be difficult to shift. Instead of synchronizing, they just slip and take a long time to match speeds.

I've never tried it. I'd just go with good quality regular oil personally. I mean, yeah you just had it rebuilt, but it's a what? 24 year old transmission at this point?

By the time it goes kabang again it'll long be a classic. And M5OD's will still probably be around... *edit: To replace it with*

Where did you hear this? (Are you generalizing about manual transmission in general, or no?) In the M5OD, it is actually recommended by many, including myself. I used the Pennzoil Syncromech Synthetic (less than $10/quart) in my manual transmission (which normally requires ATF), and it shifts smoother, quieter, and allows better lubrication through the oil galleys & passages. It is superior to ATF in that transmission.

The FM-146 may use GL-4 gear oil (NOT GL-5). Now, whether or not the synthetic gear oil causes excessive slippage, I do not know.

I'd agree and go with the regular gear oil @ $4/quart. It will be quite some time before your transmission goes out again. I put the Synchromesh in mine because my syncronization bands started to show ("feel") wear.

G'luck.

 

[Captain Ledd]

Where did you hear this? (Are you generalizing about manual transmission in general, or no?) In the M5OD, it is actually recommended by many, including myself. I used the Pennzoil Syncromech Synthetic (less than $10/quart) in my manual transmission (which normally requires ATF), and it shifts smoother, quieter, and allows better lubrication through the oil galleys & passages. It is superior to ATF in that transmission.

I've always used the specified oil in the transmissions I own. I've seen several posts on forums about people complaining that they decided to be nice to their truck and put in super high end full synthetic gear oil in their transmissions and started having problems with it going into gear once moving (yes the specified oil was 90w gear oil). It was my impression that the full synthetic stuff was more so for axle differentials.

The ATF vs fancy Gear Oil in a M5OD is a long argued point, some have success like yourself. Mine shifts perfectly acceptably and has no issues with ATF after 220,000 miles, and see little reason to change it. Personal preference I guess.